We are continuing our biochemical and biological research on basic aspects of chemotherapy with special emphasis on ways of enhancing the differential effects of the antifolates and other metabolites on normal and malignant cells. Specifically we are studying biochemical events during the transition from quiescence to replicative growth in the cell cycle. We are also studying the use of fluorine-18 labeled 5-fluorouridylate as a probe of in vivo RNA synthesis in normal and tumor tissue. This provides a means of studying the effects of various anticancer agents.